Air seems to be getting into my pump

[michmike]

hi all,

i was wondering if someone can point me to the right direction here.
if i run my pump on filter for 2-3 hours, it gradually increases the pressure from 10psi to 20psi to the point that very little water goes into the pool. in looking into this some more, i noticed that my DE filter is indeed clean and the problem is that not too much water is coming into the pump.

If i stop the pump for a second, put the filter level on WASTE for 5 seconds (5 seconds is enough for water to flow back into the pump and i can see it from the skimmer basket on the pump), and then put the pump back on FILTER i get another 2-3 hours of good water flow.

My filter grids are sparkling clean (I cleaned them up this weekend, including acid washing), the pool is clear, and backwashing does not help this.

My only assumption is that something is leaking air into my pumping system, but i dont know where to start. as an aside, if i run the pump on RECIRCULATE, it will run all day at full pressure without any issues.

any ideas?

 

[JohnT]

A pressure rise indicates a blockage after the pump. If the problem was an air leak, your pressure would drop.

It really sounds like a dirty filter, but everything you say says you have taken care of that. Have you opened the filter to verify that the backwash is removing all of the DE?

 

[duraleigh]

Yeah, michmike, JohnT is on the money. If your filter starts out at normal pressure and then the psi increases and the flow is reduced, something is plugging up that filter. That you can run it constantly on recirculate (bypassing the filter) would seem to confirm that the filter is being plugged up.....usually by unseen algae. What do your test results look like?

 

[michmike]

My test results look fine. i used to have a bad algae problem 2-3 weeks ago. but i fixed it after agreessive BBB treatments, backwashing 1 or 2 a day, and cleaning my filters this saturday (on saturday i sprayed the filters clean, then put them in a decreasing solution for 4 hours and in a 10:1 water - muriatic acid solution for another 3).

Are there algae that are not visible or green?

I did verify that backwash is getting rid of almost all DE.
Here is one other kink. if something is blocking up the filter, shouldn't that be immediate. If i run the pump on waste for 5 seconds and put it on filter again, we start at 10psi pressure again. it takes a while to go up higher again.

pool results:
TA 100
FC 15 (that's still high because i had algae and brought it to 20)
CYA 30 (this is low, and i kept it there until i am done with the backwashing and i can add cya back)
ph 7.4
CH 205

 

[michmike]

if i have unseen algaea what is your recommendation guys?
thank you by the way!

 

[duraleigh]

if something is blocking up the filter, shouldn't that be immediate. If i run the pump on waste for 5 seconds and put it on filter again, we start at 10psi pressure again. it takes a while to go up higher again.

No, it won't be immediate. Your description seems to indicate something is being filtered out of the water....dead algae, debris, etc. It is possible you can't see it in your water but there seems to be no other explanation for your psi increase and resultant flow loss. That you can clear it by going to waste would seem to indicate that just shutting the pump on and off allows the debris to fall away from the grids for a little while.

If DE filters have a disadvantage, it is that they catch EVERYTHING so they tend to plug up more quickly. Shocking a pool or clearing a really gummed up pool with a DE filter is a big task and requires a LOT of attention to the filter.

I can think of no other cause and your symptoms are classic.....your system seems to be doing EXACTLY what it is supposed to be doing.....cleaning junk (even thought you can't see it) from the water.

I think the course of action is to hold your FC up higher than normal for the next few days and continue to "bump" and backwash that filter. I believe your times in between cleanings will soon get longer and longer.

 

[michmike]

thank you! I will keep backwashing and dropping more chlorine to see if this will stop increasing the pressure at some point. I appreciate the help.